This talk will explore a number of applications of wide-area spectroscopic surveys, such as those DESI will provide, to solving key problems for imaging dark energy experiments. First, I will discuss the problem of photometric redshifts (a.k.a. photo-z’s): i.e., estimates of the redshifts of objects based only on flux information obtained through broad filters. Higher-quality, lower-scatter photo-z’s will result in smaller random errors on cosmological parameters; while systematic errors in photometric redshift estimates, if not constrained, may dominate all other uncertainties from these experiments. In this talk, I will describe the key challenges for training and calibrating photometric redshift algorithms in the next two decades, and describe how DESI can help us address these challenges. Second, I will discuss the contributions the DESI instrument can make to LSST supernova studies by measuring spectroscopic redshifts for large samples of supernova hosts, which would require comparatively modest time allocations. Finally, I will describe the new LSST Dark Energy Science Collaboration and how each of us can get involved now in preparing for this extraordinarily rich dataset.